Closed loop feedback method for electric motor

Abstract

A circuit for providing feedback regarding the torque on an AC electric motor. A sample and hold circuit provides DC voltage information regarding the voltage drop across a resistor wired in series with the windings of the motor. Reference voltage from the sample and hold circuit may be supplied to a comparator, such as an operational amplifier, along with a voltage reading from a fixed rate charging circuit. A pulse is provided to a microcontroller each time the voltage of the fixed rate charging circuit equals the reference voltage, and the fixed rate charging circuit is discharged. The microcontroller uses the frequency of the pulses to determine the load on the motor.

What is claimed is:  
     
         1 . A motor, comprising: 
 AC input;    windings connected to the AC input and configured to receive a current from the AC input;    a load resistor mounted in series with the windings; and    a sample and hold circuit connected to the load resistor and configured to sample and hold first voltage drop information representing a voltage drop across the load resistor.    
     
     
         2 . The motor of  claim 1 , further comprising an output device connected to the sample and hold circuit, the output device configured to generate a varying signal based upon changes the first voltage drop information.  
     
     
         3 . The motor of  claim 2 , wherein the output device comprises a voltage controlled oscillator.  
     
     
         4 . The motor of  claim 2 , wherein the output device comprises a comparator.  
     
     
         5 . The motor of  claim 4 , wherein the comparator is coupled to the sample and hold circuit and a fixed charge circuit.  
     
     
         6 . The motor of  claim 5 , wherein the comparator is configured to send a pulse to a microcontroller upon a voltage of the fixed charge circuit equaling a value related to the first voltage drop information.  
     
     
         7 . The motor of  claim 6 , wherein the comparator is configured to send a pulse to the microcontroller upon a voltage of the fixed charge circuit equaling the first voltage drop information.  
     
     
         8 . The motor of  claim 7 , wherein the microcontroller is configured to discharge the fixed rate charging circuit as a result of receiving the pulse.  
     
     
         9 . The motor of  claim 6 , wherein the microcontroller is configured to discharge the fixed rate charging circuit as a result of receiving the pulse.  
     
     
         10 . The motor of  claim 1 , further comprising: 
 a microcontroller connected to the sample and hold circuit and configured to receive the first voltage drop information; and    a power controller configured to receive instructions regarding speed control for the motor from the microcontroller, the instructions based upon the first voltage drop information.    
     
     
         11 . A motor, comprising: 
 AC input;    windings connected to the AC input and configured to receive a current from the AC input;    a load resistor mounted in series with the windings;    a sample and hold circuit connected to the load resistor and configured to sample. and hold first voltage drop information representing a voltage drop across the load resistor;    a comparator connected at a first input to the sample and hold circuit and having a second input;    a fixed rate charging circuit connected to the second input;    the comparator being configured to generate a pulse as a result of a voltage of the fixed rate charging circuit reaching a voltage level that is related to the first voltage drop information;    a microcontroller connected to the comparator and configured to receive the pulse and to discharge the fixed rate charging circuit as a result of receiving the pulse; and    a power controller configured to receive instructions regarding speed control for the motor from the microcontroller, the instructions based upon the frequency of pulses received by the microcontroller.    
     
     
         12 . The motor of  claim 11 , wherein the comparator is configured to send a pulse to the microcontroller upon a voltage of the fixed charge circuit equaling the first voltage drop information.  
     
     
         13 . The motor of  claim 11 , wherein microcontroller receives the pulse independent of an analog to digital converter.  
     
     
         14 . A motor, comprising: 
 AC input;    windings connected to the AC input and configured to receive a current from the AC input;    a load resistor mounted in series with the windings;    a sample and hold circuit connected to the load resistor and configured to sample and hold first voltage drop information representing a voltage drop across the load resistor;    a voltage controlled oscillator connected to the sample and hold circuit and configured to output a square wave that varies in frequency in accordance with changes in the first voltage drop information;    a microcontroller connected to the voltage controlled oscillator and configured to receive the square wave; and    a power controller configured to receive instructions regarding speed control for the motor from the microcontroller, the instructions based upon the frequency of square wave received by the microcontroller.    
     
     
         15 . The motor of  claim 14 , wherein microcontroller receives the pulse independent of an analog to digital converter.  
     
     
         16 . A motor controller, comprising: 
 a load resistor configured to be mounted in series with windings of a motor; and    a sample and hold circuit connected to the load resistor and configured to sample and hold first voltage drop information representing a voltage drop across the load resistor.    
     
     
         17 . The motor controller of  claim 16 , further comprising an output device connected to the sample and hold circuit, the output device configured to generate a varying signal based upon changes the first voltage drop information.  
     
     
         18 . The motor controller of  claim 17 , wherein the output device comprises a voltage controlled oscillator.  
     
     
         19 . The motor controller of  claim 17 , wherein the output device comprises a comparator.  
     
     
         20 . The motor controller of  claim 19 , wherein the comparator is coupled to the sample and hold circuit and a fixed charge circuit.  
     
     
         21 . The motor controller of  claim 20 , wherein the comparator is configured to send a pulse to a microcontroller upon a voltage of the fixed charge circuit equaling a value related to the first voltage drop information.  
     
     
         22 . The motor controller of  claim 21 , wherein the comparator is configured to send a pulse to the microcontroller upon a voltage of the fixed charge circuit equaling the first voltage drop information.  
     
     
         23 . The motor controller of  claim 22 , wherein the microcontroller is configured to discharge the fixed rate charging circuit as a result of receiving the pulse.  
     
     
         24 . The motor controller of  claim 21 , wherein the microcontroller is configured to discharge the fixed rate charging circuit as a result of receiving the pulse.  
     
     
         25 . The motor controller of  claim 16 , further comprising: 
 a microcontroller connected to the sample and hold circuit and configured to receive the first voltage drop information; and    a power controller configured to receive instructions regarding speed control for the motor from the microcontroller, the instructions based upon the first voltage drop information.